NLP | Storing Conditional Frequency Distribution in Redis
The nltk.probability.ConditionalFreqDist class is a container for FreqDist instances, with one FreqDist per condition. It is used to count frequencies that are dependent on another condition, such as another word or a class label. It is being used here to create an API-compatible class on top of Redis using the RedisHashFreqDist .
In the code given below, a RedisConditionalHashFreqDist class that extends nltk.probability.ConditionalFreqDist and overrides the __getitem__() method. Override __getitem__() so as to create an instance of RedisHashFreqDist instead of a FreqDist.
An instance of this class can be created by passing in a Redis connection and a base name. After that, it works just like a ConditionalFreqDist as shown in the code below :
0  1 1 ['cond1']
How it works ?
- The RedisConditionalHashFreqDist uses name prefixes to reference RedisHashFreqDist instances.
- The name passed into the RedisConditionalHashFreqDist is a base name that is combined with each condition to create a unique name for each RedisHashFreqDist.
- For example, if the base name of the RedisConditionalHashFreqDist is ‘condhash’, and the condition is ‘cond1’, then the final name for the RedisHashFreqDist is ‘condhash:cond1’.
- This naming pattern is used at initialization to find all the existing hash maps using the keys command.
- By searching for all keys matching ‘condhash:*’, user can identify all the existing conditions and create an instance of RedisHashFreqDist for each.
- Combining strings with colons is a common naming convention for Redis keys as a way to define namespaces.
- Each RedisConditionalHashFreqDist instance defines a single namespace of hash maps.
RedisConditionalHashFreqDist also defines a clear() method. This is a helper method that calls clear() on all the internal RedisHashFreqDist instances. The clear() method is not defined in ConditionalFreqDist.